eccodes

This crate contains safe high-level bindings for ecCodes library. Bindings can be considered safe mainly because all crate structures take ownership of the data in memory before passing the raw pointer to ecCodes.

Currently only reading of GRIB files is supported.

As the API of this crate differs significantly from the API of ecCodes library make sure to read its documentation. Read this section to learn more about design decisions of this crate.

If you want to see more features released quicker do not hesitate to contribute and check out Github repository. All submitted issues and pull requests are welcome.

ecCodes is an open-source library for reading and writing GRIB and BUFR files developed by European Centre for Medium-Range Weather Forecasts.

Because ecCodes supports mainly Linux platforms, this crate is not tested on other architectures.

Usage

ecCodes installation

This crate uses eccodes-sys with default options to link ecCodes. Check eccodes-sys website for more details on how it links the library.

The recommended way to install ecCodes on your computer is using your package manager. For example, on Ubuntu you can use apt-get:

sudo apt-get install libeccodes-dev

Alternatively, you can install the library manually from source in suitable directory following this instructions.

Then add the lib/pkgconfig directory from your ecCodes installation directory to the PKG_CONFIG_PATH environmental variable. If ecCodes have been compiled as shared library you will also need to specify LD_LIBRARY_PATH. For example:

export PKG_CONFIG_PATH=<your_eccodes_path>/lib/pkgconfig
export LD_LIBRARY_PATH=<your_eccodes_path>/lib

Accessing GRIB files

This crate provides an access to GRIB file by creating a CodesHandle and reading with it messages from the file.

The CodesHandle can be constructed in two ways:

The main option is to use new_from_path() function to open a file under provided path with filesystem, when copying whole file into memory is not desired or not necessary.
Alternatively new_from_memory() function can be used to access a file that is already in memory. For example, when file is downloaded from the internet and does not need to be saved on hard drive. The file must be stored in bytes::Bytes.

Data (messages) inside the GRIB file can be accessed using the FallibleIterator by iterating over the CodesHandle.

The FallibleIterator returns a KeyedMessage structure which implements some methods to access data values. The data inside KeyedMessage is provided directly as Key or as more specific data type.

Example

// We are reading the mean sea level pressure for 4 gridpoints
// nearest to Reykjavik (64.13N, -21.89E) for 1st June 2021 00:00 UTC 
// from ERA5 Climate Reanalysis

// Open the GRIB file and create the CodesHandle
let file_path = Path::new("./data/iceland.grib");
let product_kind = ProductKind::GRIB;

let handle = CodesHandle::new_from_path(file_path, product_kind)?;

// Use iterator to get a Keyed message with shortName "msl" and typeOfLevel "surface"
// First, filter and collect the messages to get those that we want
let mut level: Vec<KeyedMessage> = handle
    .filter(|msg| {

    Ok(msg.read_key("shortName")?.value == Str("msl".to_string())
        && msg.read_key("typeOfLevel")?.value == Str("surface".to_string()))
    })
    .collect()?;

// Now unwrap and access the first and only element of resulting vector
// Find nearest modifies internal KeyedMessage fields so we need mutable reference
let level = &mut level[0];

// Get the four nearest gridpoints of Reykjavik
let nearest_gridpoints = level.find_nearest(64.13, -21.89)?;

// Print value and distance of the nearest gridpoint
println!("value: {}, distance: {}", 
    nearest_gridpoints[3].value, 
    nearest_gridpoints[3].distance);

Writing GRIB files

The crate provides a basic support for setting KeyedMessage keys and writing GRIB files. The easiest (and safest) way to create a new custom message is to copy existing one from other GRIB file, modify the keys and write to new file.

You can find a detailed example of setting keys and writing message to file in the documentation.

Features

docs - builds the create without linking ecCodes, particularly useful when building the documentation on docs.rs. For more details check documentation of eccodes-sys.

To build your own crate with this crate as dependency on docs.rs without linking ecCodes add following lines to your Cargo.toml

[package.metadata.docs.rs]
features = ["eccodes/docs"]

Crate safety

Because the ecCodes library API heavily relies on raw pointers simply making ecCodes functions callable without unsafe block would still allow for creation of dangling pointers and use-after-free, and the crate would not be truly safe. Therefore these bindings are rather thick wrapper as they need to take full ownership of accessed data to make the code safe. Having the data and pointers contained in dedicated data structures is also an occasion to make this crate API more convenient to use than the original ecCodes API (which is not really user-friendly).

Roadmap

(Functions from ecCodes API wrapped at given stage are marked in parentheses)

Reading GRIB files
- Creating CodesHandle from file and from memory (codes_handle_new_from_file, codes_handle_delete)
- Iterating over GRIB messages with Iterator (codes_get_message, codes_get_message_copy, codes_handle_new_from_message, codes_handle_new_from_message_copy)
- Reading keys from messages (codes_get_double, codes_get_long, codes_get_string, codes_get_double_array, codes_get_long_array, codes_get_size, codes_get_length, codes_get_native_type)
- Iterating over key names with Iterator (codes_grib_iterator_new, codes_grib_iterator_next, codes_keys_iterator_get_name, codes_keys_iterator_rewind, codes_grib_iterator_delete)
- Finding nearest data points for given coordinates (codes_grib_nearest_new, codes_grib_nearest_find, codes_grib_nearest_delete)
Writing GRIB files (codes_set_double, codes_set_long, codes_set_string, codes_set_double_array, codes_set_long_array,codes_set_length)
Reading and writing BUFR files

License

The ecCodes library and these bindings are licensed under the Apache License Version 2.0

IAPark/eccodes